Weft-detecting method and apparatus



June 13, 1967 R. o. GIBB WEFT-DEI'ECTING METHOD AND APPARATUS 5 Sheets-$heet 1 Filed Jan. 12 1965 INVENTOR ROBERT O. GIBB ATTORNEYS 5 Sheets-Sheet 2 FIG. 6

R. O. GIBB BOW 72 SKEW 8 WANDER *"74 WEFT-DETECTING METHOD AND APPARATUS TRANSDUCER A TRANSDUCER 5 TRANSDUCER A TRANSDUCER C June 13, 1967 Filed Jan. 12 1965 g 'ro TRANSDUCER B j HG. l0

June 13, 1967 R. o. GIBB 3,324,718

WEFT-DETECTING METHOD AND APPARATUS Filed Jan. 12, 1965 5 Sheets-Sheet 5 FIG. H

INVENTOR. ROBERT 0. GIBB ATTORNEYS United States Patent 3,324,718 WEFT-DETECTING METHOD AND APPARATUS Robert 0. Gibb, Bridgewater, Mass, assignor to Mount Hope Machine Company, Incorporated, Taunton, Mass, a corporation of Massachusetts Filed Jan. 12, 1965, Ser. No. 429,192 Claims. (Cl. 73-159) ABSTRACT OF THE DESQLOSURE A method and apparatus for detecting an abnormal non-perpendicular relation of the weft to the warp of a traveling woven Web made of any filamentary material. The web is tensioned along a transverse axis to create curved distortion patterns, and the slope of the curves of the warp is measured at the tensioning axis. The measurement is made by one or more single caster wheel detectors, skew distortion being detectable by one, and bow distortion by two, detectors.

This application is a continuation-in-part of US patent application S.N. 253,551 filed Jan. 24, 1963, now aban doned.

The present invention is an improvement of the skewdetecting method and apparatus disclosed and claimed in United States Patent No. 2,795,029, issued June 11, 1957, to John Douglas Robertson and John L. Broomfield, entitled, Skew Detecting Method and Apparatus. That patent discloses a method for detecting weft abnormalities, which comprises the steps of subjecting the web to transverse or weftwise tension thereby to produce incidental distortion of the warp elements, and detecting the induced distortions, which directly and accurately reflect any distortion of the weft elements.

The apparatus disclosed by the aforementioned patent for carrying out this process includes tandem pairs of detectors, preferably including caster wheels, each connected to a variable reluctance magnetic pick-off of a type familiar to those skilled in the art, which are positioned inwardly from the margins or selvages of the web. The wheels of each tandem pair contact substantially the same warp element at points spaced apart lengthwise of the web. The differential in response between the wheels of each tandem pair is utilized to control correction devices for removing any detected skew or bow of the weft elements. The differential response might, for example, be signalled by connecting the pick-offs of each tandem pair of detectors as an alternating current resistance bridge in which any imbalance is reflected as an output signal, indicating by its phase the sense of a weft abnormality, and by its amplitude the magnitude of the distortion. This system has been found to operate satisfactorily and to provide accurate signals for the correction of abnormalities; but is both mechanically and electrically somewhat complex. It is necessary to provide at least one tandem pair of detector wheels with cooperating variable inductance means for the detection of skew alone; and at least two sets of tandem detector wheels with ancillary equipment must be provided for the detection of both skew and bow abnormalities.

I have discovered that the method disclosed by the aforementioned patent may be performed with singlewheel detectors, provided these are located on an axis of maximum transverse stretching of the web; and have devised improved weft-detecting apparatus incorporating these single detector wheels and utilizing improved means for analyzing their output signals for the control of cor rection apparatus. It is accordingly the primary object of my invention to afford an improved method and apparatus for detecting abnormalities in the weft elements of a travel- 3,324,718 Patented June 13, 1967 ing woven web. Additional objects of my invention include the provision of a weft-detecting method and apparatus which affords continuous detection signals accurately indicative of both bow and skew abnormalities of the weft elements; and the simplification, without loss of accuracy and sensitivity, of the mechanical and electrical systems utilized in such apparatus. Further objects and advantages of the invention will appear at the following description proceeds.

Briefly stated, I may carry out my invention in a preferred form of apparatus by mounting one or more single detectors, each having only one detector wheel instead of tandem wheels, to detect the direction of movement of warp elements of a traveling Web at a tensioning axis of maximum stretch. Web-pulling means, which may be niprolls, are arranged to stretch the moving web transversely along that axis. In one form, each detector acts in conjunction with a pair of Web-pulling means closely spaced on either side of that detector; in other forms, two detectors contact the web intermediate 21 pair of Web-pulling means, one detector being positioned in proximity to each of them.

While one single-wheel detector may be utilized for indicating only skew abnormalities, both skew and bow abnormalities can be measured simultaneously by providing two single detectors which engage the web at transversely-spaced intervals on the tensioning axis. Means are provided for producing simultaneous output signals representing the algebraic sum and difference of the signals of the two single detectors; these output signals, as will be explained hereinafter, are accurate measures of skew and bow abnormalities, respectively.

This arrangement of two detector wheels is not adapted to distinguish lateral wandering movement of the web from a skewed distortion, but in many applications the extent of wandering movement is so slight that no dis tinction need be made. However, for those applications in which substantial wandering movement cannot be avoided, I provide a single additional detector wheel which is arranged to contact the web at a position spaced longitudinally away from the tensioning axis, so that it is unaffected by bowed or skewed distortions of the weft elements, and delivers an output signal only in response to bodily movement of the web in a lateral direction. This signal is amplified to double the value of the signals of the primary detector wheels and algebraically subtracted from the sum of the primary signals indicating skew; thus any false signal arising from wandering is cancelled automatically. It should be noted that the wander signal need not be applied to correct the output signal indicating bow, since this signal is unaffected by wandering movement, being in itself the algebraic difierence between the signals of two detector wheels.

The method of detecting weft abnormalities according to this invention is based upon the phenomena that induced distortion of the Warp elements along a tensioning axis of maximum stretch lateral to the web, appears as a local curvature of each warp element; and that each such curve includes a point of zero slope with respect to the direction of web travel. Slope in this sense is defined as the tangent of the angle formed by any incremental segment of a distorted warp element to the normal, undisturbed warp threads, i.e., the direction of cloth travel. Further, the location of this point of zero slope with respect to the tensioning axis is found to vary according to the condition of the weft elements. In a normal rightangular relationship of the weft elements, the curves are centered on the tensioning axis, and the point of zero slope is found to coincide with the tensioning axis. But if there is an abnormal condition of the weft elements, this point of zero slope will be displaced forwardly or ing the slope of the induced curvature of warp elements at the tensioning axis of maximum transverse stretch. Displacement of the induced curvatures from the tensioning axis -will result in the appearance of positive or negative slopes at this axis, indicating an abnormal weft condition.

These slopes are preferably detected at two points spaced apart laterally of the web, for detection at two such points makes it possible to discriminate bowed and skewed abnormalities. A bowed abnormality is reflected by equal slopes at both points, but the slopes are of opposite senses (i.e., opposite angular deviations from the direction of web travel). A skewed abnormality is reflected by equal slopes of the same sense or angular deviation.

The magnitude of these angular displacements or slopes is a measure of the magnitude of a weft distortion. Their relative senses or directions are a measure of the nature of the distortion, and distinguish between a skew, in which the weft elements are substantially straight but are not perpendicular to the warp elements, or a bow, in which the weft elements are curved from end to end, or a combination of these characteristic distortions.

The improved method further includes the steps of algebraically adding, and at the same time algebraically subtracting, the detected slopes; two error signals result, of which the additive signal indicates skewed abnormality and the subtractive signal indicates bowed abnormality. These signals may be applied to control conventional corrective mechanisms.

In a modification of this method, spurious signals produced by lateral wandering movement of the web are cancelled by detecting the slope of warp elements at a point on the web spaced away from the tensioning axis so that the induced curvatures do not appear, by doubling the value of the slope to produce an error signal, and by algebraically subtracting this error signal from the additive skew-indicating signal.

may be gained from the following detailed description of preferred embodiments, referring to the accompanying drawings, in which:

FIG. 1 is a diagrammatic representative of a traveling woven web in which the weft elements are in proper rightangular relationship to the warp elements, together with means at the opposite edges of the web for stretching it transversely, and two single detector wheels located on the axis of the tensioning means according to the invention;

FIG. 2 is a view generally similar to FIG. 1, but showing the effect produced when the woven elements are skewed with their ends which are at the right-hand edge of the web leading their ends at the left-hand edge;

FIG. 3 is a view generally similar to FIG. 1, but showing the effect produced by the stretching when the weft elements are bowed with their ends near the edges of the web leading the central portions;

FIG. 4 is a view generally similar to FIG. 1, showing a modification in which a third detector wheel is utilized for correcting the output signals of the principal detectors, so that lateral Wandering movement does not produce a spurious signal indicating skew;

FIG. 5 is a sectional view in side elevation of a detector unit with supporting means;

FIG. 6 is a plan view of the detector unit, taken along line 6-6 in FIG. 5 looking in the direction of the arrows, together with a schematic representation of a transducer circuit for generating an output signal;

FIG. 7 is a wiring diagram for coupling the trans ducers of two signal detectors to provide output signals indicating both how and skew;

FIGS. 8 and 9 are diagrams indicating the relative phases and magnitudes of the transducer signals of the circuit of FIG. 7, and the output signals which are produced, when the weft elements are skewed and bowed, respectively;

FIG. 10 is a wiring diagram for the connection of the transducers of two primary detectors and of a further detector as shown in FIG. 4, for producing output signals from which errors arising from lateral wandering movement are cancelled; and

FIG. 11 is a diagrammatic representation of a traveling web with a modified arrangement of detectors and webpulling means.

Referring to FIGS. 14, the improved method of weft detection is illustrated diagrammatically as it may be performed by the improved apparatus. A traveling woven web 10 comprises warp elements 12 extending in a direction of longitudinal web movement indicated by the arrow, and weft elements 14. In a normal relationship as shown, the weft elements extend perpendicularly to the warp elements. The web is tensioned transversely to the direction of travel along an axis AA by suitable means such as will not interfere with the longitudinal movement; these are illustrated as pairs of nip-rolls 16, each rotatably supported at an angle to the direction of travel by means of a suitable axle 18. These means may be as more fully described in the aforementioned US. Patent No. 2,795,029. The rolls act to tension the web along the axis AA, and in so doing incidentally distort the warp elements, on either side of the web centerline, to curved .forms which are centered on the axis.

The axis AA is the axis of maximum transverse stretch, and does not coincide with the axes of rotation of the niprolls, but is slightly downstream at the points where the rolls release the web. The web is somewhat compressed, which accounts for this displacement.

In each curve, a point of zero slope with respect to the direction of travel coincides with the axis AA. A pair of detectors 20 are arranged intermediate the centerline and the opposite selvages 21 of the web. The detecting elements of the detectors shown comprise caster wheels 22, which are arranged to engage warp elements at the axis AA. In the undistorted web condition shown, the wheels 22 extend parallel to the direction of web travel, with no relative angular displacement, and thus measure a zero slope.

In the event that an abnormality of the weft elements 14 occurs, the induced curvatures of the warp elements 12 are correspondingly displaced longitudinally of the web from their erstwhile centered relation to the tensioning axis, and the caster wheel detectors are angularly displaced to measure the angular deviations or slopes of the Warp elements at the tensioning axis. FIG. 2 is illustrative of a skew distortion, in which the right-hand ends of the weft elements lead their left-hand ends. It will be observed that the points of zero slope of one set of curves in the Warp elements induced by the nip-roll at the lefthand selvage are now all displaced forwardly of the tensioning axis, while the points of zero slope of a second set of curves induced by the nip-roll at the righthand selvage are disposed rearwardly of this axis. This is occasioned by the nip-rolls pulling on separate weft elements longitudinally displaced from one another, so that the distorted portion of the web tends to rotate counter-clockwise. The detector at the left-hand edge is relatively displaced rearwardly from the weft element 14a on which the left-hand nip-roll pulls, while the detector at the right-hand edge is relatively displaced forwardly of the weft element 14b on which the right-hand nip roll pulls. The detectors, each following the local slope of the induced curvatures, are angularly displaced in the same sense and to the same extent.

An algebraic subtraction of the measured slopes results in a null signal, correctly indicating that no how is present. However, an algebraic addition of the slopes produces a positive signal indicating by its sense the nature of the skew, i.e., that the right-hand edges of the weft elements are leading; and by its magnitude the extent of the skewed condition.

A bowed condition is illustrated in FIG. 3, in which the end portions of the weft elements lead their centers in the direction of Web travel. In consequence of the bowed condition, both nip-rolls 16 pull directly upon the same weft element 140, which causes the induced curvatures to be displaced rearwardly of the tensioning axis AA. correspondingly, the detector wheels 22 on the axis AA are angularly displaced in opposite senses and to substantially the same extent. Algebraic addition of these signals accordingly produces a null signal, indicating that no skew is present; while algebraic subtraction results in a signal indicating the magnitude and sense of the bowed abnormality.

it will thus be apparent that by detecting the slopes of the induced curvatures on the traverse tensioning axis at two points spaced across the center line of the web, and by both algebraically adding and subtracting the measured slopes, output signals are produced which are independently indicative of bowed and skewed abnormalities, or combinations of both.

In many cases, a moving web is maintained in a uniform lateral position, or deviates only very slightly. A signal results from a lateral movement of the web which erroneously indicates a skewed condition, but this may be tolerated where the movement is small. However, there are many other situations in which substantial lateral wandering movement cannot be avoided, and for this purpose a modified method and apparatus can afford a corrected signal from which any signal occasioned by such movement is cancelled. This modification is illustrated in FIG. 4, in which the slope of the wrap elements is detected not only at two points located on the tensioning axis, but also at a third point longitudinally spaced away from the region of induced curvature.

For this purpose, a third detector 24 is provided, having a caster wheel 26 engaging the web at a point spaced forwardly from the detectors 20, and located approximately on the center line of the web. The web is illustrated in a normal condition, but with a lateral movement taking place in conjunction with the longitudinal movement, as indicated vectorially by the arrows. This movement produces a temporary equi-angular displacement of each detector wheel, which is indicative of the lateral velocity, rather than of the slope of the warp elements, which remain parallel to the direction of web travel at the points of detection. If a correction were not afforded, the temporary angular displacement of the detectors 2!) would appear as an erroneous skew-indicating signal. However, the angular displacement of the error detector 24, which is of the same sense and magnitude as the signal of each detector 20, is doubled in value and then algebraically subtracted from the sum of the angular displacements of the detectors 2!}, so that the erroneous output signal is cancelled.

It will be understood that upon the occurrence of an actual weft abnormality, the error detector will cancel only that portion of the skew signal which reflects lateral wandering movement, and the net skew-detection signal will be accurate. It should be noted that the bow-detection signal is unaifected by a lateral wandering movement, since this signal is obtained by algebraically subtracting the slopes indicated by the two detectors 20; the signals arising from lateral movement are of the same sense and magnitude for both detectors, and will be nullified 'by the subtraction.

Each of the single caster wheel detectors 20 and 24 may be constructed substantially as shown and described in the aforementioned United States Patent No. 2,795,029, with the omission of the second or tandem caster wheel and its associated inductance coils. A construction of this kind is shown in FIGS. 5 and 6. A detector 20 is organized within a unit housing 30 having bearing means 32 for rotatably supporting a pivot shaft 34. The pivot shaft carries a fork 36 in which a caster wheel 22 is rotatably mounted. An elongated arm 38 is secured to the pivot shaft by means of a split clamp 40 and a clamping screw 42, and carries at its free end a steel armature 44, The armature projects within the air cores of a pair of coils 46, which are mounted within the unit housing beneath a cover member 48.

The detector 20 is adjustably supported on a rod and a screw shaft 52 by means of a bracket 54, which is slidably mounted on both the rod and the screw shaft. The bracket includes a vertically-adjustable depending leg 56, to the lower end portion of which one end of the unit housing 30 is pivotally connected at 58. A stop screw is adjustable in the leg 56 for limiting counter-clockwise gravitational rotation of the unit housing, as viewed in FIG. 5, about the pivotal connection at 58. By properly adjusting the stop screw 60, and vertically adjusting the leg 56 in the bracket by means of set screws 62, the caster wheel 22 may be adjusted to provide a desired degree of engagement with the web 16. The bracket 54 may be secured in any selected position along the rod 50 by set screws 64 or the like. It will be understood by reference to the aforementioned patent that the screw shaft 52 serves primarily to adjust the positions of the nip-rolls 1-6 laterally with respect to the selvages of the web.

For producing a signal indicative of the angular displacement of the detector wheels 22, and consequently indicative of the sense and magnitude of the slopes of the warp elements, the coils 46 of each detector are connected in a transducer circuit schematically indicated in FIG. 6. The coils are connected by lead-s 65 and 66 in a bridge circuit with the branches of a center-tap power supply transformer 67, the center-tap of the transformers secondary winding being connected by lead 69 to an output coil 68, and a center-tap lead 71 between the two coils 46 also being connected to the output coil. Thus, any angular displacement of the detector wheel from the neutral position shown will result in an imbalance of the bridge, and production of a voltage in the output coil 68 which indicates by its phase the sense or angular direction of the detected slope, and by its magnitude the extent of this slope.

As previously described, the output voltages of the transducers of each detector 20 are algebraically added and subtracted to provide output signals independently indicative of skew and bow, respectively. Circuitry for this purpose is illustrated in FIG. 7, in which the transducers of two detectors 20 are designated as A and B. The output coils 68 form the primaries of transformers each having a pair of equivalent secondary windings and 72. The pairs 70 are connected in series-aiding relation, and provide an output voltage which represents an algebraic addition of the inputs from the individual transducers, i.e., a skew signal. The pair of windings 72 are connected in series-opposing relation, and thus atiord an output voltage which represents the algebraic difierence between the transducer inputs, i.e., a bow signal.

Examples of the process of addition and subtraction of the transducer voltages are graphically illustrated in FIGS. 8 and 9. First assuming a normal perpendicular relationship of the warp and weft elements of the web, the transducers produce no output signal. Signals indicating a skewed condition are illustrated in FIG. 8, such as are produced when the detectors are displaced in the same angular sense; these signal voltages are in phase with one another. Therefore, their summation provides a positive indication of a skewed condition. In the case of a pure skewed abnormality without bow, and assuming that the detectors are spaced substantially equally from their adjacent selvages, the magnitudes of the two transducer signals are substantially equal and no substractive or how signal is produced.

In the case of a bowed condition as illustrated in FIG. 9, the transducer signals are of substantially equal magnitude, but the opposite directions of angular displacement of the detector wheels causes these signals to be relatively reversed in phase. Therefore, a summation of the signals produces a null skew signal, but the algebraic subtraction provides a signal indicative of a bowed abnormality.

A modification of the signal circuit is shown in FIG. 10 for use with the modified form of apparatus shown in FIG. 4, which corrects the skew signal for lateral web movement. This circuit includes a third transducer C associated with the error detector 24. The subtractive signal circuit is identical with that of FIG. 7, including two output coils 72 connected in series-opposing relationship. The output coil 68 of the transducer C forms the primary winding of a transformer in which the secondary winding 74 has sufiicient turns to double the output voltage with respect to any amplification in the coils 70. The winding 74 is connected in series-opposing relation to the windings 70, which remain in series-aiding relation. Thus, an error signal arising in the coil 74 from lateral wandering movement of the web, cancels the additive output voltage produced in the detectors 20 by this wandering movement, and the resulting skew signal is automatically corrected.

It will be understood that the bow-and skew-indicating signals produced by this detector may be used merely to show the condition of the web, or may directly control correction devices for removing bowed and skewed abnormalities from the moving web.

A modified arrangement is shown in FIG. 11, in which parts similar to those of the preceding embodiments are similarly numbered. Each detector 20 acts in conjunction with an individual pair of web-pulling means comprising nip-rolls 16, and is normally centered between them. Thus each detector is located on an individual tensioning axis; as shown, these axes may conveniently coincide, although this is not necessary. Each pair of oppositely-angled nip-rolls straddling one detector is preferably located in close proximity to that detector.

This arrangement completely isolates each detector from lateral forces in the remaining width of the web, and lends itself to the use of a multiplicity of detectors so that a more complete and accurate analysis of complex distortions can be obtained. And in general, a more uniform flow pattern is secured because the nip-rolls tend to .shape the pattern both upstream and down, whereas in the previously-described arrangements the downstream pattern is aifected materially by the elasticity, tension, speed, and other conditions of the web itself. This arrangement therefore gives some increase in accuracy and uniformity of detection. It also decreases the adverse affect of a slack web condition on the shaping of the flowpattern, and reduces wrinkling of the web by the niprolls.

While I 'have shown and described preferred embodiments of my invention by way of illustration, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the true spirit and scope of the invention. -1 therefore intend to define my invention in the appended claims without limitation to specific details of construction and arrangement referred to in the foregoing description.

What I claim and desire to secure by Letters Patent of the United States is:

1. The method of detecting an abnormal non-perpendicular relation of the transverse elements to the longitudinal elements of a longitudinally-traveling woven web, which comprises subjecting a portion of the width of the traveling web to continuous tension applied substantially equally in opposite directions along a transverse tensioning axis of maximum transverse stretch, thereby to stretch said portion of the web into local curves which, in the normal relation of said elements, are centered on said transverse axis and have points of zero slope with respect to the direction of travel of the web which coincide with said axis, detecting the slope of said curves at said axis, and establishing an output signal in response to the detected slope as a measure of abnormality of said lateral elements.

2. The method of detecting an abnormal non-perpendicular relation of the transverse elements to the longitudinal elements of a longitudinally-traveling woven web, which comprises subjecting at least a substantial portion of the width of the traveling web to continuous tension applied substantially equally in opposite directions along a transverse tensioning axis of maximum transverse stretch, thereby to stretch said portion of the web with incidental regional distortion of longitudinal elements of the web into local curves which, in the normal relation of said elements, are centered on said transverse axis and have points of zero slope with respect to the direction of travel of the web which coincide with said axis, detecting the slope of said curves at two laterally-spaced points lying upon said axis, establishing two signals in response to the detected slopes, and algebraically adding and subtracting said signals simultaneously to produce composite signals for indicating, respectively, skewed and bowed abnormal relationship of said elements.

3. The method recited in claim 2, together with the further steps of simultaneously detecting the slope of longitudinal elements with respect to the direction of travel of the web at a point spaced away from the region of curved distortion of the longitudinal elements, establishing a further signal in response to the simultaneouslydetected slope, and algebraically subtracting said further signal from the composite signal produced by addition of said two signals to derive a net signal corrected for error introduced by lateral movement of said web.

4. Apparatus for detecting an abnormal non-perpendicular relation of the transverse elements to the longitudinal elements of a longitudinally-traveling woven web, comprising web-pulling means constructed and arranged to continuously transversely stretch a portion of the width of the traveling web along a tensioning axis of maximum transverse stretch, said axis extending transversely of the direction of travel of the web, thereby to induce a region of wave-like curves in the longitudinal elements, each of which curves has a point of zero slope with respect to the direction of travel of said web which lies on said axis when said transverse elements are in a normal condition relative to said longitudinal elements, and which points of zero slope are displaced longitudinally of said web from said axis when said transverse elements are oriented abnormally, and a detector located on said axis to detect the slope of said curves at said axis for indicating the condition of said transverse elements, said detector including circuit means for producing signals indicative of the magnitude and sense of the slope detected thereby.

5. Apparatus as recited in claim 4, in which said detector is located on said axis at substantially the lateral center of said stretched web portion.

6. Apparatus as recited in claim 4, together with second web-pulling means constructed and arranged to continuously transversely stretch a further portion of the web along a further tensioning axis, a second detector located on said further axis to detect the slope of curves in said further portion, said second detector including circuit means for producing signals indicative of the magnitude and sense of the slope detected thereby, and further circuit means for algebraically adding and subtracting the signals of said first-mentioned and said second detectors simultaneously to produce independent output signals indicative of skewed and bowed abnormalities, respectively, of said transverse elements.

7. Apparatus for detecting an abnormal non-perpendicular relation of the transverse elements to the longitudinal elements of a longitudinally-traveling woven web, comprising web-pulling means constructed and arranged to continuously transversely stretch a portion of the width of the traveling web along a tensioning axis of maximum transverse stretch, said axis extending transversely of the direction of travel of the web, thereby to induce a region of wave-like curves in the longitudinal elements, each of which curves has a point of zero slope with respect to the direction of travel of said web which lies on said axis when said transverse elements are in a normal condition relative to said longitudinal elements, and which points of zero slope are displaced longitudinally of said web from said axis when said transverse elements are oriented abnormally, a pair of detectors each located on said axis in spaced-apart relation oppositely across the longitudinal centerline of said stretched web portion and intermediate lateral edges thereof to detect the slope of said curves at said axis for indicating the condition of said transverse elements, each of said detectors including circuit means for producing signals indicative of the magnitude and sense of the slopes detected thereby, and further circuit means for algebraically adding and subtracting said signals simultaneously to produce independent output signals indicative of skewed and bowed abnormalities, respectively, of said transverse elements.

8. Apparatus as recited in claim 7, together with a third detector spaced away from said region of curves to detect the slope of longitudinal elements of the web which are not curved by said Web-pulling means, said third detector including means for producing a further signal indicative of the magnitude and sense of the slope detected thereby, said further circuit means including means for amplifying said further signal to double its magnitude and means for algebraically subtracting the resulting doubled signal from the One of said output signals indicative of skewed abnormalities to correct said one output signal for error introduced by lateral movement of said Web.

9. Apparatus as recited in claim 7, in which each of said detectors comprises a single caster wheel pivotally supported to engage longitudinal elements of the web and to follow said longitudinal elements in tangential relation to a curve therein.

10. Apparatus as recited in claim 7, in which said signal-producing circuit means of each of said detectors includes an output coil, and said further circuit means comprises two pairs of inductance windings, each pair being inductively coupled with one of said output coils, first members of each pair being connected in seriesaiding relation to produce one of said output signals indicative of skewed abnormality, and second members of each pair being connected in series-opposing relation to produce the other of said output signals indicative of bowed abnormality.

References Cited UNITED STATES PATENTS 2,795,029 6/ 1957 Robertson et al.

DAVID SCHONBERG, Primary Examiner. 

1. THE METHOD OF DETECTING AN ABNORMAL NON-PERPENDICULAR RELATION OF THE TRANSVERSE ELEMENTS TO THE LONGITUDINAL ELEMENTS OF A LONGITUDINALLY-TRAVELING WOVEN WEB, WHICH COMPRISES SUBJECTING A PORTION OF THE WIDTH OF THE TRAVELING WEB TO CONTINUOUS TENSION APPLIED SUBSTANTIALLY EQUALLY IN OPPOSITE DIRECTIONS ALONG A TRANSVERSE TENSIONING AXIS OF MAXIMUM TRANSVERSE STRETCH, THEREBY TO STRETCH SAID PORTION OF THE WEB INTO LOCAL CURVES WHICH, IN THE NORMAL RELATION OF SAID ELEMENTS, ARE CENTERED ON SAID TRANSVERSE AXIS AND HAVE POINTS OF ZERO SLOPE WITH RESPECT TO THE DIRECTION OF TRAVEL OF THE WEB WHICH COINCIDE WITH SAID AXIS, DETECTING THE SLOPE OF SAID CURVES AT SAID AXIS, AND ESTABLISHING AN OUTPUT SIGNAL IN RESPONSE TO THE DETECTED SLOPE AS A MEASURE OF ABNORMALITY OF SAID LATERAL ELEMENTS. 